storing user data for 24 hours

Hi, I cannot figure out how this site http://www.kingsofchaos.com/page.php?id=293994 makes it so anyone who goes their can only be recorded once every 24 hours. Are they going by IP or what? I would like to use something like this on my site, but I was thinking that using an IP wouldn't be that accurate...:/

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If you run run a WordPress, you understand the potential headaches you may face when updating your plugins and themes. Do you choose to update on the fly and risk taking down your site; or do you set up a staging, keep it in sync with your live site and use that to test updates?

Foreword (July, 2015)
Since I first wrote this article, years ago, a great many more people have begun using the internet. They are coming online from every part of the globe, learning, reading, shopping and spending money at an ever-increasing ra…